Silicon carbide (SiC) has overwhelmingly superior basic physical properties for use as power semiconductor devices, including a wide band-gap, high dielectric breakdown, thermal conductivity, chemical stability, and high saturation drift velocity. At the present, silicon-base materials are widely used in power devices. SiC is expected to play the main role for next generation power devices, with some SiC power semiconductor devices being marketed.
At the present, commercially available SiC single crystal wafers are all produced by the sublimation process. When power devices are manufactured using SiC single crystal wafers obtained by the sublimation method, their performance is not necessarily sufficient. This is because it is not easy to form a SiC single crystal with fewer defects. Since the crystal growth by the sublimation process is a precipitation phenomenon from a gas phase, the growth rate is low and the temperature management in a reaction space is difficult. As a result of the recent intensive efforts for improvement by research and development institutes, the density of micropipes is reduced. However, lattice defects, which have an impact upon electric characteristics of devices, such as threading screw dislocations, threading edge dislocations, and basal plane dislocations, are still included at high densities. Of the current commercial SiC single crystal wafers produced by the sublimation process, wafers of small area of not greater than 3 mm by 3 mm for SiC power devices are mass produced, though in low yields, because the influence of dislocations rarely develops, but wafers of larger area for high-current devices are not still mass produced because of outstanding leak current.
Under the circumstances, the method for producing SiC single crystal by the solution process of crystal growth of SiC becomes attractive. See Patent Documents 1 to 3. The solution process for producing SiC single crystal includes a variety of techniques, which are generally divided into four classes: traveling solvent method (TSM), slow cooling technique (SCT), vapor liquid solid (VLS), and top seeded solution growth (TSSG). See Non-Patent Document 1. In general, the solution process implies the TSSG.